a) Field of the Invention
The present invention relates to manufacture techniques for semiconductor devices, and more particularly a manufacture method and system for a semiconductor device capable of forming a thin oxynitride film on the surface of a silicon wafer.
b) Description of the Related Art
Demands for higher integration and higher operation speed of CMOS semiconductor devices are high. In order to meet such requests, it is necessary to make finer transistors constituting CMOS devices and improve a driving force. In the case of a p-channel MOS transistor, it is necessary to use a boron doped gate electrode for realizing a surface channel type and to make a thin gate insulating film.
As the gate insulating film is thinned, a phenomenon is likely to occur that boron ions doped into the gate electrode pass through the gate insulating film and reach the substrate channel region. It is known that in order to prevent this phenomenon, it is effective to use an oxynitride film as the gate insulating film.
Shallow trench isolation (STI) instead of LOCOS isolation has been proposed in order to manufacture high integration semiconductor devices. For the shallow trench isolation, a process of forming shallow grooves (trenches) in a wafer surface and then filling the insides of trenches with insulating material is performed before forming semiconductor elements. As a result, the active region surrounded by the isolation region has a convex cross sectional structure.
A thermal oxidation film to be formed on the convex area has stress so that the insulating film becomes hard to be grown, i.e., a thinning phenomenon occurs. If the thinning phenomenon occurs, it is difficult to make the thickness of a gate insulating film formed in the active region have reliably a constant value. In order to prevent the thinning phenomenon, it is known that wet oxidation is effective.
As compared to dry oxidation, wet oxidation provides a high oxidation speed so that it can effectively form an oxide film at a lower temperature. In order to form an oxynitride film through wet oxidation, base oxidation is first performed to form a thin oxide film, and then nitrogen is introduced into this oxide film.
For example, a wet oxide film is formed on a plurality of wafers at the same time in a vertical batch diffusion furnace, and thereafter nitrogen is introduced into the oxide film in the unit of wafer, i.e. wafer by wafer, by using a single wafer annealing system.
As described above, it is effective to use an oxynitride film as the gate insulating film in order to manufacture micro-channel MOS transistors having a high driving force. However, a manufacture process of forming a gate insulating film of a thin oxynitride film is complicate and the manufacture throughput lowers. Therefore, this process is not suitable for mass production.
It is desired to use NO or N2O as nitrogen containing gas when nitrogen is introduced into an oxide film. However, presently available systems are not capable of using such gas.